LearnDash is a great LMS in and of itself. The course building, organizing, and managing software gives you plenty of robust options to work your way through the course creation process.
However, e-learning is a dynamic field. It does not do to remain static, content with only a handful of features. LearnDash opens new vistas in course building for you through its extensions, where every feature brings a plethora of options for you to utilize, whether course-related, student-related, or instructor-related.